1. Field of the Invention
The present invention is related to a method for forming contacts of an electrical connector, a press die for practicing the method, and an electrical contact obtained by the method.
2. Description of Prior Art
As the conditions of signal transmission between different electronic devices are getting severer and severer (for example, high speed and density transmission under heated and corrosive atmosphere), the quality of contacts of connectors for achieving an electrical connection between the devices is required to be higher and higher. To meet the requirement, dimension accuracy and surface quality of an engaging section of the contact for achieving the electrical connection seek endless improvement.
The contact, after a mechanical forming, is subject to an electrical plating process whereby a noble metal is coated to the engaging section of the contact to improve electrical conductivity and thus signal transmission quality of the contact. To form the engaging section with a required precise dimension and a smooth surface so that it can accurately and reliably engage with a conductive portion of a complementary device under certain conditions, i.e., sufficient normal force, low mating force, etc., and can be uniformly and firmly plated with the noble metal so that the coating can stand severe environment, i.e., corrosive and heated environment, the engaging section is usually subject to a shaving operation by a die insert of a press die for forming the contact.
Conventionally, a profile of the die insert for the shaving operation is subject to a profile grinding by using a diamond grinding wheel to have a surface of the profile with a roughness of about 0.12 Ra. The engaging section thus formed can meet the old use in which the required specifications for the contacts to meet are moderate. However, for the newly developed electronic devices, for example, a RIMM connector which is used for connecting a Rambus memory module to a mother board, the contacts formed by the conventional technology cannot meet the severer requirements. To shave the engaging section of the contact by the die insert processed by the conventional technology causes the engaging section not smooth enough so that the coating of the noble metal thereon is not sufficiently uniform and firm. A non-uniform coating of the noble metal on the engaging section causes the surface of the coating is not smooth enough so that a large mating force is needed when the complementary device is inserted into the connector. A large mating force may cause the engaging section to warp. A non-firm coating of the noble metal on the engaging section causes the noble metal to easily separate from the contact when the connector is under a heated/corrosive environment or when the contact is repeatedly engaged/disengaged with/from the complementary device.
Finally, when shaving the engaging section by the conventionally processed, relatively rough die insert, the engaging section can not obtain the required precise dimension whereby the required normal force should be exerted to the conductive portion of the complementary device by the engaging section may not be achieved, which in turn may deteriorate the signal transmission quality between the connector and the complementary device.
Hence, an improvement is needed to eliminate the above mentioned defects of prior art.
Accordingly, an objective of the present invention is to provide a press die for forming a contact of a connector, wherein a die insert of the press die for shaving a mating device engaging section of the contact has an extraordinarily smooth surface so that the mating device engaging section can have a corresponding smooth surface and precise dimension after the shaving process. The engaging section after the shaving process can be very uniformly and firmly coated with a layer of noble metal thereon by a electrical plating process.
A further objective of the present invention is to provide a method for forming a contact of an electrical connector by utilizing a press die having a die insert with an extraordinary smooth surface on a portion thereof for conducting a shaving operation to an engaging section of the contact. Thus, the engaging section of the contact for electrically engaging with a conductive portion of a complementary device can have an extraordinary precise dimension and smooth surface. A noble metal layer can be firmly and evenly coated to the engaging section of the contact formed in accordance with the method.
A still further objective of the present invention is to provide a contact which can meet the severer requirements for the newly developed electrical connector such as RIMM connectors for connecting newly developed electronic devices, for example, Rambus memory modules to mother boards.
To achieve the above objectives, a profile of a die insert for shaving an engaging section of a contact of an electrical connector during a mechanical forming of the contact by blanking a metal sheet is subject to a final finishing process by an ultrasonic machining after a profile grinding process. The ultrasonic machining consists of several successive steps using diamond particles dispersed in liquid as the working agent, wherein the diamond particles have the following correspondingly different grit sizes in the different steps: 600#, 1000#, 2000#, 5000#, and finally 8000#.